With governments and governmental agencies imposing increasingly lower emissions limits from internal combustion engines, attention has been directed to a number of strategies for reducing emissions of regulated combustion by-products, such as particulate matter (also known as soot), nitrous oxides (NOx) and other greenhouse gases. One strategy has been to improve the efficiency and quality of combustion for engines fuelled with conventional liquid fuels, to reduce the amount of such emissions produced by combustion and to add exhaust treatment systems such as catalytic converters and filters, to trap certain combustion products and reduce the amounts of such emissions that are ultimately released into the environment. For example, particulate filters can trap particulate matter and catalytic exhaust treatment systems can convert greenhouse gases into benign substances such as elemental nitrogen and oxygen. Recent increases in global oil prices make conventionally fuelled engines more costly to operate.
Another strategy is to substitute most or all conventional liquid fuel with a cleaner burning gaseous fuel such as, for example, methane, ethane, propane, lighter flammable hydrocarbon derivatives, hydrogen, or natural gas or other blends usable as a gaseous fuel. In addition to being cleaner burning, many of these fuels can be generated from renewable sources. When substituting a cleaner burning gaseous fuel for most of the fuel, a small amount of liquid fuel can be used as a pilot fuel, for assisting with ignition of the gaseous fuel, as well as for lubrication and cooling in the injection valve. A challenge associated with this approach is that it requires the supply of two different fuels to the fuel injection valves.
Fuel injection valves for injecting a single fuel directly into a combustion chamber are well known. There are a number of known arrangements for supplying a single fuel to an injection valve. For example, a bore formed in the cylinder head can serve as a fuel rail for delivering high pressure fuel directly to the injection valve. In another embodiment, piping external to the cylinder head can serve as the fuel rail, and such piping can be connected to an inlet into the fuel injection valve where it protrudes above the cylinder head. In still other arrangements, fuel is delivered through a fuel rail provided by piping external to the cylinder head, and high pressure fuel is delivered to the fuel injection valve via a fuel connector that extends through a bore in the cylinder head. An advantage of this last arrangement is that fuel that leaks from the fuel connector is kept away from the cylinder head cover where it might contaminate the lubrication oil.
To reduce the development cost of producing an engine that is fuelled with a gaseous fuel and a different pilot fuel, dual fuel injection valves have been developed that can fit within the bore normally occupied by a conventional single-fuel injection valve. For example, such valves are disclosed in co-owned U.S. Pat. Nos. 5,996,558, 6,073,862, 6,298,833, 6,336,598, 6,439,192, and 6,761,325. This avoids the time and cost associated with developing a custom cylinder head that might otherwise be needed to supply two different fuels to an engine, and because no modifications are needed to the cylinder head it can be manufactured at the same cost as the mass produced cylinder heads that are made for engines fuelled with conventional liquid fuels. In preferred embodiments the two fuels are delivered to the fuel injection valve separately. An advantage of delivering the fuels separately to the fuel injection valve is that the fuel proportions can be adjusted depending upon engine operating conditions. The fuels can either be mixed inside the injection valve or injected separately into the engine combustion chamber. An additional advantage of injecting the fuel separately is that greater flexibility is possible with respect to the timing for the injection of each fuel and this is a variable that can be manipulated to improve combustion quality.
The applicant has developed dual fuel injection valves for a Cummins™ model ISX engine which has formed within its cylinder head three bores associated with each bank of cylinders, two of which can be utilized as high pressure fuel supply rails for supplying two separate fuels under high pressure to the fuel injection valves. The third bore can be used to drain hydraulic fluid from hydraulic actuators. However, unlike the model ISX engine, many other engines are designed to use external piping for supplying fuel to the fuel injection valves so they do not have bores provided within their cylinder heads that can serve as fuel rails. For these engines a problem with delivering two fuels to fuel injection valves using external piping is that the additional piping associated with the second fuel rail adds complexity and there are spatial limitations for the piping and the connections between the fuel rail and the fuel injection valves. In addition, as mentioned already with respect to the fuel injection valves, it is desirable to reduce or obviate the need for modifications to the cylinder head.
Accordingly, there is a need for an arrangement for supplying two different fuels to a fuel injection valve, for engines that are not designed with a cylinder head that has internal bores that can serve as fuel rails. In addition, it would be advantageous if the two different fuels can be delivered to fuel injection valves from two fuel rails that are external to the cylinder head without requiring substantial modifications to the cylinder head.